1. Field of the Invention
The present invention relates to a power transmission V belt for use in a continuously variable transmission for an automobile. More particularly, the present invention relates to a power transmission V belt having a loop-shaped metallic belt and a plurality of metallic V blocks mounted on the loop-shaped metallic belt successively in the longitudinal direction thereof and engageable in V-shaped grooves of driver and driven V pulleys.
2. Description of the Relevant Art
There have recently been proposed power transmission V belts for use in automotive continuously variable transmissions, the V belts comprising a loop-shaped or endless metallic belt and a plurality of metallic V blocks mounted on the loop-shaped metallic belt successively in the longitudinal direction thereof. When such a V belt is trained around driver and driven V pulleys, the V blocks are received in the V-shaped grooves of these driver and driven V pulleys.
One example of such a power transmission V belt is disclosed in Japanese Patent Laid-Open Publication No. 60-101337 published June 5, 1985. The loop-shaped metallic belt of the disclosed V belt comprises a plurality of stacked steel belt members. The V belt also includes cylindrical rollers each positioned inwardly of the metallic belt and inserted between adjacent V blocks. These rollers have axes oriented perpendicularly to a plane in which the V belt lies. The V blocks have arcuate recesses defined in their front and rear surfaces in the longitudinal direction of the V belt, each roller being received in a confronting pair of arcuate recesses. There are as many rollers on the V belt as the number of the V blocks. In each confronting pair of the arcuate recesses which receives a roller, one of the recesses has an arcuate roller-receiving surface of a larger radius of curvature than that of the roller, whereas the other arcuate recess has an arcuate roller-receiving surface of a smaller radius of curvature than that of the roller.
When the V blocks engage in the V-shaped groove of the driver pulley, the pulley applies reactive forces radially outwardly to the slanted opposite surfaces of the V blocks for thereby enabling the rollers to be wedged against the arcuate roller-receiving surfaces having a larger radius of curvature. The reactive forces thus applied serve to increase the gap between adjacent V blocks, namely, the radius of an arcuate path along which the V blocks rotate about the axis of the driver pulley. Under this condition, the radially outward surfaces of the V blocks are pressed into frictional engagement with the radially inward surface of the metallic belt, which is therefore forced by the V blocks to rotate with the driver pulley. The loop-shaped metallic belt is now under tension to transmit power from the driver pulley to the driven pulley. The steel belt members of the metallic belt are pressed together while the metallic belt is under tension.
As described above, the V blocks and the metallic belt are held in mutually frictional engagement at the radially outward surfaces of the V blocks and the radially inward surface of the belt. When transmitting torque, therefore, these mutually frictionally engaging surfaces are caused to slip with respect to each other. The mutually frictionally engaging surfaces tend to slip to a larger extent and hence to produce greater heat and wear when a larger load is imposed or when there is a larger torque change. This also holds true for the mutually frictionally engaging surfaces of the steel belt members of the metallic belt which are subject to high tension.
One solution to the above problem would be to supply oil to oil grooves defined in at least one of the frictionally contacting surfaces of the V blocks and the metallic belt, for thereby forming an oil film between the frictionally contacting surfaces. This proposal would be effective when the V blocks are forced against the metallic belt under low pressure. However, the oil film would be apt to be lost under high contact pressure. Another problem would be increased contact pressure, applying excessive stresses.
An alternative solution would be to supply oil under pressure to the contacting surfaces of the V blocks and the metallic belt. It would be extremely difficult, however, to achieve a structure for supply oil under pressure since there are gaps between the blocks.
Slippage of the laminated metallic belt itself would be solved by supplying oil to oil grooves defined in the steel belt members. This arrangement is not preferable for the metallic belt that undergoes high tension since the mechanical strength of the metallic belt would be reduced by the oil grooves.
The present invention has been made in an effort to eliminate the aforesaid drawbacks of the conventional power transmission V belts.